The quality of electrical signal transmission is important and even critical in many aspects of modern life. Although the invention is discussed herein in special detail regarding audio and video signals, persons of ordinary skill in the art will understand that it has utility in a broad range of technologies and applications. Moreover, even though much of the discussion herein focuses on components of audio, and video (including, by way of example and not by way of limitation, speaker and interconnect cables), persons of ordinary skill in the art will understand that the invention can provide many benefits to many types of analog and digital signals.
For many individuals, technological innovations in audio and video signal generation, transmission, and reproduction have made the “home entertainment theater” video and/or audio systems the entertainment medium of choice. Those systems commonly include numerous separate electrical devices that need to transmit signals to and among each other. In addition to conventional “audio system” components (receivers, CD players, turntables, etc.), the visual experience has been enhanced with the advent of large screen televisions that include flat LCD and plasma screens. These entertainment packages are commonly coupled with multiple speakers for surround sound. The systems are sometimes integrated with computers and with speaker systems throughout the owner's home.
Independently of (or in addition to) the full “home theater” concept, audio systems designers strive to provide high quality sound to music aficionados. The dominant and common way that video and audio components are interconnected and communicate with each other is via cables. As such, one particular area of interest for system designers in enhancing audio/video reproduction is cable technology
Enhanced cable technology facilitates signal communication between electrical components, which in turn results in appreciable improvement in the signal quality and resulting audio/video experience. In video systems, improved signal quality between electrical components may be observed in increased accuracy of video reproduction, thus video clarity is enhanced and the viewer's overall visual experience is enriched. In audio systems, improved signal quality between electrical components can reduce audio distortion heightening the overall fidelity of the music heard by the listener.
In other (non-video/audio) applications such as data communication (or indeed, any cable used to send electrical signals), the accuracy and reliability of signal transmission can similarly be improved by better cable technology. Persons of ordinary skill in the art will understand that this applies for both digital and analog signals.
Cable technology includes several aspects in which advances have been pursued, with varying degrees of success. These aspects include the materials used in the construction of cable elements and various arrangements of active and passive cable elements. Active elements include conductors used for signal transmission while passive elements may include dielectric/insulation materials specifically used to electrically isolated signal conductors, or metal to shield/protect the overall cable construction.
Other design and performance aspects include cable “run-in.” Cable “run-in” refers to the process by which a cable eventually comes to a “steady” electrical state (including a relatively “stable” condition of the cable's dielectric material). The cable's transmission properties change as its dielectric material is exposed to various electrical charges. Similar to the charging of a capacitor, transmitting a desired signal over a cable can impose a potential across the cable's dielectric material that changes material properties of the dielectric. The process of “charging” the cable impacts the cable's transmission properties. However, once the cable is charged, it is in a relatively steady or stable electrical state.
Cable “run-in” is often mistakenly referred to as “break-in.” However, “break-in” is more properly used to describe a mechanical change, e.g., engines, loudspeakers, and phono cartridge suspensions “break-in” during their initial periods of use. In contrast, cable “run-in” may be somewhat analogous to engine oil that warms during engine use to more efficiently and effectively protect the engine from damage cause by heat and/or friction. Just as that oil warming can reoccur every time that the engine is started, cable “run-in” (the gradual forming of the cable's transmission properties) can recur every time a signal is imposed on the cable.
In other words, and as indicated above, cables of this type may be thought of as long capacitors being gradually charged (i.e., “formed”) by the electrical signal as the signal is communicated along a conductor surrounded by an insulating dielectric material. Most, if not all, conventional cables take some significant amount of time to “run-in” or optimize their performance characteristics through this dielectric biasing. By one estimate, it may take up to 300 hours of charging to establish an optimal (relatively steady) electrical field within a given cable. In addition, each time the audio or video signal is removed (i.e., an electrical device(s) is turned off), the electrical field in the cable dissipates and must be re-established when the electrical device(s) are turned back on (using the engine oil analogy, the oil must be warmed up each time the engine is started). In other words, the “run-in” process is repeated each time the source that created the “run-in” condition is removed and then reestablished.
As a consequence, the audio or video connoisseur may never (or may only very rarely) enjoy optimum sound quality using conventional cables, as the electric field is typically never fully established. Among other things, the home theater system may be turned off after a few hours or less of listening/viewing, precluding the cables from ever reaching an optimal “steady state.” Even if the audio or video system is left in a stand-by mode, typically no signal propagation takes places through the cable, and once again, the electrical field collapses and the cables must be “run-in” again upon the next activation of the system.
Alternatively, the cable may be biased by a source other than the voltage varying electrical signal as that signal passes through the cable (see, for example, U.S. Pat. No. 5,307,416 to Martin). However, because that “other” biasing voltage is applied to conductors that are themselves in the electrical signal path, systems such as Martin's require the addition circuits such as digital gates, blocking capacitors, filtering devices and the like, to isolate the electrical devices' unbiased signal from the “other” biasing voltage. As such, Martin's approach introduces additional components that may increase manufacturing and/or consumer costs, and decrease system reliability.
Accordingly, there is a need for an improved system and method for biasing the dielectric of a cable connected between electrical devices, to eliminate the “run-in” problems mentioned above without the complications of a system such as described in the aforementioned Martin patent.
Other cables (such as Synergistic Research's Active Shielding) have shielding to reject external RF noise and use a blocking capacitor for “stronger” RF shielding. To the extent that such “active shielding” technology may provide some biasing of the cable dielectric as a by-product of its intended shielding purpose, it does so with shortcomings such as some of those in the aforementioned Martin patent—its “biasing circuit” is part of the signal path.